356 HOW TO SEE WITH THE MICROSCOPE. 



nished at the suggestion of the author, who invariably 

 orders them for his friends and pupils. The instru- 

 ment is thus rendered efficient for all the ordinary pur- 

 poses of the working microscopist : 



Supplemental revolving stage $1 00 



Sub-stage adapter, to carry condenser, society screw. ... 1 00 

 Eye-piece adapters, ready to carry solid cells, each 1 00 



STAGE MICROMETERS, TEST PLATES, ETC., BY W. 

 A. ROGERS, CAMBRIDGE MASS. 



Mr. Rogers has just completed his new machine, in the con- 

 struction of which several important improvements have been 

 secured. We cheerfully add. our endorsement as to the regu- 

 larity and delicacy of his rulings. One of his plates, ruled up to 

 120,000 lines to the inch, now in our possession, is a marvel of art. 

 Owing to the extreme shallowness of Mr. Rogers' finer rulings, 

 they are more difficult tests than similar bands by Kobert. Mr. 

 Rogers furnishes a great variety of work. Some of his regular 

 plates may be thus described : 



Stage Micrometer, consisting of 10 lines, 100, and 10 

 lines, 1,000 to the inch $1 25 



Stage Micrometer, consisting of 25 lines, 200 to the inch, 

 10 lines, 1,000, 10 lines, 2,000, 10 lines, 4,000, 10 lines, 

 5,000, 10 lines, 10,000, 10 lines, 20,000, and 10 lines, 30,000 

 to the inch 4 00 



Stage Micrometers, ruled 1,000, 10,000,20,000, 30,000, 40,000 

 and 50,000 to the inch 500 



Same as above, to 60,000 6 00 



" " to 70,000, $7.00; to 80,000, $8.CO; to 90,000 900 



" " to 100,000 10 00 



(Closer rulings by special contract.) 



Standard half-inches, with 50 subdivisions of l-100thinch 

 and 10 subdivisions in the centre of l-100th inch : 3 00 



Standard centimeters, with 100 subdivisions 4 00 



(At double the above prices Mr. Rogers furnishes a 

 complete discussion of the errors of the plates, and a 



